Exploring the validity and limitations of the Mott-Gurney law for charge-carrier mobility determination of semiconducting thin-films
Exploring the validity and limitations of the Mott-Gurney law for charge-carrier mobility determination of semiconducting thin-films
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DOI：
10.1088/1361-648x/aaabad
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发表时间：
2018-03-14
影响因子：
2.7
通讯作者：
Nelson, Jenny
中科院分区：
文献类型：
--
作者：
Rohr, Jason A.;Moia, Davide;Nelson, Jenny
利用漂移扩散模拟，我们研究了通常用于确定载流子迁移率的单载流子器件中暗电流的电压依赖性。对于低电压和高电压，电流随外加电压线性增加。低压时的线性电流主要是由于器件中间的空间电荷引起的，而高压时的线性电流则是由于高度注入引起的载流子饱和引起的。因此，这些电压下的电流密度不遵循Mott和Gurney导出的经典平方定律，并且我们表明，对于无陷阱器件，仅在中间电压下，可以观察到空间电荷限制漂移电流的斜率接近2。我们表明，根据半导体层的厚度和注入势垒的大小，两种线性电流-电压状态可以主导整个电压范围，而中间的莫特-格尼状态可以收缩或消失。在这种情况下，特别是对于用于探测有机半导体的典型单载流子器件的厚度和注入障碍，使用莫特-格尼定律进行有意义的分析将无法实现，因为无法再实现平方律拟合，从而导致迁移率被大大低估。讨论了当用于本征半导体分析时何时预期偏离莫特-格尼定律的一般准则。
Using drift-diffusion simulations, we investigate the voltage dependence of the dark current in single carrier devices typically used to determine charge-carrier mobilities. For both low and high voltages, the current increases linearly with the applied voltage. Whereas the linear current at low voltages is mainly due to space charge in the middle of the device, the linear current at high voltage is caused by charge-carrier saturation due to a high degree of injection. As a consequence, the current density at these voltages does not follow the classical square law derived by Mott and Gurney, and we show that for trap-free devices, only for intermediate voltages, a space-charge-limited drift current can be observed with a slope that approaches a value of two. We show that, depending on the thickness of the semiconductor layer and the size of the injection barriers, the two linear current-voltage regimes can dominate the whole voltage range, and the intermediate Mott-Gurney regime can shrink or disappear. In this case, which will especially occur for thicknesses and injection barriers typical of single-carrier devices used to probe organic semiconductors, a meaningful analysis using the Mott-Gurney law will become unachievable, because a square-law fit can no longer be achieved, resulting in the mobility being substantially underestimated. General criteria for when to expect deviations from the Mott-Gurney law when used for analysis of intrinsic semiconductors are discussed.